From what little I know, the people in hazmat suits are those who are in an area where they could pick up radioactive particles on their clothing; the suits can be shucked as part of an exit process to keep all of the radioactive particles confined. The hazmat suits do little to protect against the actual radiation, most of that is mitigated by limiting the time you can spend in the area.
There have been a few "dirty jobs" type shows which have shown this process in action: when replacing a turbine on a nuclear generator, there was a literal line in the floor everyone watched - materials and people could only move in one direction with respect to that line without a lengthy cleaning and inspection. There's also a few Veritasium YouTube videos about a visit to Chernobyl which goes into detail about the exposure limits.
I would speculate that either the folks in hazmat suits had to traverse more contaminated areas to get where they are standing, or the activity will potentially dislodge radioactive material into the air around them, or there are unmarked hot spots where radiation levels are higher.
